1. Field of the Invention
Many industrial operations involve the transfer of bulk liquids from storage tanks into tank trucks, tank cars, or other storage vehicles. Usually, such transfers are made through a liquid delivery system that is common to two or more storage tanks holding different liquids. The present invention is directed to such a delivery system, and is particularly concerned with providing means for transferring any of several liquids without contaminating the liquid being transferred with any significant amount of a previously delivered liquid. It is also concerned with providing means for minimizing evaporative losses and for recovering vapors during such transfer.
2. Description of the Prior Art
In industries that sell an assortment of bulk liquid chemicals, transfer of such chemicals from storage tanks into tank trucks, railroad tank cars, or other storage vehicles is frequently necessary. In most cases, such transfers are made through a single liquid delivery or dispensing system. Strangely, however, such systems seldom have means integrated therewith for measuring the amount of liquid transferred therethrough; instead, the amount of liquid so transferred is determined by weighing the storage vehicle before and after the filling of its storage tank, or by filling said storage tank up to a predetermined liquid level.
The primary reason that the amount of transferred liquid is measured by such methods is that the most widely employed liquid metering means, the positive displacement, nutating-piston meter, if employed in such a liquid delivery system, would, during the subsequent draining of said system, entrap a significant amount of liquid in both the nutating meter itself and its associated piping. The total amount of liquid so entrapped may range between about 3 and 5 gallons, assuming the meter is of commercial size. Hence, a liquid delivery system incorporating such a meter could not be effectively utilized to transfer any of a plurality of liquids because, after a first liquid is transferred, none of the others could be transferred through the same system without being contaminated with a significant amount of said first liquid.
Another problem inherent in using commercially available liquid delivery systems resides in the vapor removal means usually employed therewith to remove vapors emitted from the liquids entering the vehicle storage tank. The presently accepted means for removing such vapors entail means for (a) sealing the gases within the storage tank from the surrounding atmosphere and (b) drawing said gases out of the storage tank during the filling thereof with liquid. While such means are effective for removing the vapors, they also totally obstruct a workman's view into the vehicle storage tank, thereby increasing the likelihood of flooding the vapor removal means with liquid or filling the entire vehicle storage tank with the wrong liquid. Moreover, environmental protection agencies in some states, including the State of California, require that vapor withdrawal from vehicle storage tanks in the manner described (i.e., by sealing the vapors from the surrounding atmosphere) be accomplished at a pressure substantially less than atmospheric, thus resulting in the volatilization and loss of more of the liquid entering the storage tank than would occur if the vapor removal were accomplished at essentially atmospheric pressure.
It is accordingly an object of this invention to provide a liquid delivery system capable of transferring an accurately measured amount of a liquid from one vessel to another while avoiding contamination of said liquid with any significant amount of a liquid previously transferred through the same system. Another object is to provide, in such a delivery system, means for collecting vapors evolved from the receiving vessels while permitting visual observation of the operation. A further object is to provide, in such a system, means for minimizing the amount of liquid vaporized during delivery. Other objects and attendant advantages will be apparent from the following detailed description of the invention.